Apparatus and method for measuring color

ABSTRACT

Methods in a spectral measurement apparatus are disclosed. Light is received with a plurality of sensors. Each sensor generates an output signal having a frequency proportional to an intensity of light received by the sensor. First, second and third signals are generated each having a frequency proportional to an intensity of light received by a sensor of a wavelength or spectral band. A spectral characteristic of the received light is determined based on at least the first, second and third signals, which are are coupled to a processing element and input in parallel. The spectral characteristic is determined based on measuring a frequency or period of the at least first, second and third signals. Spectral data based on the determined spectral characteristic is generated by the processing element and displayed on a display device for perception by a viewer or transmitted to a data interface for transmission to an electronic device external to the spectral measurement apparatus.

This application is a continuation of U.S. application Ser. No.11/523,763, filed Sep. 18, 2006, now U.S. Pat. No. 7,400,404, which is acontinuation is a continuation of U.S. application Ser. No. 10/302,459,filed Nov. 22, 2002, now U.S. Pat. No. 7,113,283, which is acontinuation of U.S. application Ser. No. 09/397,156 filed Sep. 15,1999, now U.S. Pat. No. 6,490,038, which is a continuation of U.S.application Ser. No. 09/267,825 filed on Mar. 12, 1999, now U.S. Pat.No. 6,307,629, which is a continuation of U.S. application Ser. No.08/909,989 filed on Aug. 12, 1997, now U.S. Pat. No. 5,883,708, which isa continuation of U.S. application Ser. No. 08/581,851 filed on Jan. 2,1996, now U.S. Pat. No. 5,745,229.

FIELD OF THE INVENTION

The present invention relates to devices and methods for measuring thecolor of objects, and more particularly to devices and methods formeasuring the color of teeth, fabric or other objects or surfaces with ahand-held probe that presents minimal problems with height or angulardependencies.

BACKGROUND OF THE INVENTION

Various color measuring devices such as spectrophotometers andcolorimeters are known in the art. To understand the limitations of suchconventional devices, it is helpful to understand certain principlesrelating to color. Without being bound by theory, Applicants provide thefollowing discussion.

The color of an object determines the manner in which light is reflectedfrom the surface of the object. When light is incident upon an object,the reflected light will vary in intensity and wavelength dependent uponthe color of the surface of the object. Thus, a red object will reflectred light with a greater intensity than a blue or a green object, andcorrespondingly a green object will reflect green light with a greaterintensity than a red or blue object.

One method of quantifying the color of an object is to illuminate itwith broad band spectrum or “white” light, and measure the spectralproperties of the reflected light over the entire visible spectrum andcompare the reflected spectrum with the incident light spectrum. Suchinstruments typically require a broad band spectrophotometer, whichgenerally are expensive, bulky and relatively cumbersome to operate,thereby limiting the practical application of such instruments.

For certain applications, the broad band data provided by aspectrophotometer is unnecessary. For such applications, devices havebeen produced or proposed that quantify color in terms of a numericalvalue or relatively small set of values representative of the color ofthe object.

It is known that the color of an object can be represented by threevalues. For example, the color of an object can be represented by red,green and blue values, an intensity value and color difference values,by a CIE value, or by what are known as “tristimulus values” or numerousother orthogonal combinations. It is important that the three values beorthogonal; i.e., any combination of two elements in the set cannot beincluded in the third element.

One such method of quantifying the color of an object is to illuminatean object with broad band “white” light and measure the intensity of thereflected light after it has been passed through narrow band filters.Typically three filters (such as red, green and blue) are used toprovide tristimulus light values representative of the color of thesurface. Yet another method is to illuminate an object with threemonochromatic light sources (such as red, green and blue) one at a timeand then measure the intensity of the reflected light with a singlelight sensor. The three measurements are then converted to a tristimulusvalue representative of the color of the surface. Such color measurementtechniques can be utilized to produce equivalent tristimulus valuesrepresentative of the color of the surface. Generally, it does notmatter if a “white” light source is used with a plurality of colorsensors (or a continuum in the case of a spectrophotometer), or if aplurality of colored light sources are utilized with a single lightsensor.

There are, however, difficulties with the conventional techniques. Whenlight is incident upon a surface and reflected to a light receiver, theheight of the light sensor and the angle of the sensor relative to thesurface and to the light source also affect the intensity of thereceived light. Since the color determination is being made by measuringand quantifying the intensity of the received light for differentcolors, it is important that the height and angular dependency of thelight receiver be eliminated or accounted for in some manner.

One method for eliminating the height and angular dependency of thelight source and receiver is to provide a fixed mounting arrangementwhere the light source and receiver are stationary and the object isalways positioned and measured at a preset height and angle. The fixedmounting arrangement greatly limits the applicability of such a method.Another method is to add mounting feet to the light source and receiverprobe and to touch the object with the probe to maintain a constantheight and angle. The feet in such an apparatus must be wide enoughapart to insure that a constant angle (usually perpendicular) ismaintained relative to the object. Such an apparatus tends to be verydifficult to utilize on small objects or on objects that are hard toreach, and in general does not work satisfactorily in measuring objectswith curved surfaces.

The use of color measuring devices in the field of dentistry has beenproposed. In modern dentistry, the color of teeth typically arequantified by manually comparing a patient's teeth with a set of “shadeguides.” There are numerous shade guides available for dentists in orderto properly select the desired color of dental prosthesis. Such shadeguides have been utilized for decades and the color determination ismade subjectively by the dentist by holding a set of shade guides nextto a patient's teeth and attempting to find the best match.Unfortunately, however, the best match often is affected by the ambientlight color in the dental operatory and the surrounding color of thepatient's makeup or clothing and by the fatigue level of the dentist.

Similar subjective color quantification also is made in the paintindustry by comparing the color of an object with a paint referenceguide. There are numerous paint guides available in the industry and thecolor determination also often is affected by ambient light color, userfatigue and the color sensitivity of the user. Many individuals arecolor insensitive (color blind) to certain colors, further complicatingcolor determination.

In general, color quantification is needed in many industries. Several,but certainly not all, applications include: dentistry (color of teeth);dermatology (color of skin lesions); interior decorating (color ofpaint, fabrics); the textile industry; automotive repair (matching paintcolors); photography (color of reproductions, color reference ofphotographs to the object being photographed); printing and lithography;cosmetics (hair and skin color, makeup matching); and other applicationsin which it useful to measure color in an expedient and reliable manner.

With respect to such applications, however, the limitations ofconventional color measuring techniques typically restrict the utilityof such techniques. For example, the high cost and bulkiness of typicalbroad band spectrometers, and the fixed mounting arrangements or feetrequired to address the height and angular dependency, often limit theapplicability of such conventional techniques.

Moreover, another limitation of such conventional methods and devicesare that the resolution of the height and angular dependency problemstypically require contact with the object being measured. In certainapplications, it may be desirable to measure and quantify the color ofan object with a small probe that does not require contact with thesurface of the object. In certain applications, for example, hygienicconsiderations make such contact undesirable. In the other applicationssuch as interior decorating, contact with the object can mar the surface(such as if the object is coated with wet paint) or otherwise causeundesirable effects.

In summary, there is a need for a low cost, hand-held probe of smallsize that can reliably measure and quantify the color of an objectwithout requiring physical contact with the object, and also a need formethods based on such a device in the field of dentistry and otherapplications.

SUMMARY OF THE INVENTION

In accordance with the present invention, devices and methods areprovided for measuring the color of objects, reliably and with minimalproblems of height and angular dependence. A handheld probe is utilizedin the present invention, with the handheld probe containing a number offiber optics. Light is directed from one (or more) light source fiberoptics towards the object to be measured, which in certain preferredembodiments is a central light source fiber optic (other light sourcearrangements also may be utilized). Light reflected from the object isdetected by a number of light receiver fiber optics. Included in thelight receiver fiber optics are a plurality of perimeter fiber optics.In certain preferred embodiments, three perimeter fiber optics areutilized in order to take measurements at a desired, and predeterminedheight and angle, thereby minimizing height and angular dependencyproblems found in conventional methods. In certain embodiments, thepresent invention also may measure translucence and fluorescencecharacteristics of the object being measured, as well as surface textureand/or other surface characteristics.

The present invention may include constituent elements of a broad bandspectrophotometer, or, alternatively, may include constituent elementsof a tristimulus type calorimeter. The present invention may employ avariety of color measuring devices in order to measure color in apractical, reliable and efficient manner, and in certain preferredembodiments includes a color filter array and a plurality of colorsensors. A microprocessor is included for control and calculationpurposes. A temperature sensor is included to measure temperature inorder to detect abnormal conditions and/or to compensate for temperatureeffects of the filters or other components of the system. In addition,the present invention may include audio feedback to guide the operatorin making color measurements, as well as one or more display devices fordisplaying control, status or other information.

With the present invention, color measurements may be made with ahandheld probe in a practical and reliable manner, essentially free ofheight and angular dependency problems, without resorting to fixtures,feet or other undesirable mechanical arrangements for fixing the heightand angle of the probe with respect to the object.

Accordingly, it is an object of the present invention to addresslimitations of conventional color measuring techniques.

It is another object of the present invention to provide a method anddevice useful in measuring the color of teeth, fabric or other objectsor surfaces with a hand-held probe of practical size that does notrequire contact with the object or surface.

It is a further object of the present invention to provide a colormeasurement probe and method that does not require fixed positionmechanical mounting, feet or other mechanical impediments.

It is yet another object of the present invention to provide a probe andmethod useful for measuring color that may be utilized with a probesimply placed near the surface to be measured.

It is a still further object of the present invention to provide a probeand method that are capable of determining translucency characteristicsof the object being measured.

It is a further object of the present invention to provide a probe andmethod that are capable of determining surface texture characteristicsof the object being measured.

It is a still further object of the present invention to provide a probeand method that are capable of determining fluorescence characteristicsof the object being measured.

Finally, it is an object of the present invention to provide a probe andmethod that can measure the area of a small spot singularly, or thatalso can measure irregular shapes by moving the probe over an area andintegrating the color of the entire area.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more fully understood by a description ofcertain preferred embodiments in conjunction with the attached drawingsin which:

FIG. 1 is a diagram illustrating a preferred embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a cross section of a probe inaccordance with a preferred embodiment of the present invention;

FIG. 3 is a diagram illustrating an arrangement of fiber optic receiversand sensors utilized with a preferred embodiment of the presentinvention;

FIGS. 4A to 4C illustrate certain geometric considerations of fiberoptics;

FIGS. 5A and 5B illustrate the light amplitude received by fiber opticlight receivers as a function of height from an object;

FIG. 6 is a flow chart illustrating a color measuring method inaccordance with an embodiment of the present invention;

FIGS. 7A and 7B illustrate a protective cap that may be used withcertain embodiments of the present invention;

FIGS. 8A and 8B illustrate removable probe tips that may be used withcertain embodiments of the present invention;

FIG. 9 illustrates a fiber optic bundle in accordance with anotherpreferred embodiment of the present invention;

FIGS. 10A, 10B, 10C and 10D illustrate and describe other fiber opticbundle configurations that may be used in accordance with yet otherpreferred embodiments of the present invention;

FIG. 11 illustrates a linear optical sensor array that may be used incertain embodiments of the present invention;

FIG. 12 illustrates a matrix optical sensor array that may be used incertain embodiments of the present invention;

FIGS. 13A and 13B illustrate certain optical properties of a filterarray that may be used in certain embodiments of the present invention;

FIGS. 14A and 14B illustrate examples of received light intensities ofreceivers used in certain embodiments of the present invention; and

FIG. 15 is a flow chart illustrating audio tones that may be used incertain preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in greater detail with referenceto certain preferred embodiments.

With reference to FIG. 1, an exemplary preferred embodiment of a colormeasuring system and method in accordance with the present inventionwill be described.

Probe tip 1 encloses a plurality of fiber optics, each of which mayconstitute one or more fiber optic fibers. In a preferred embodiment,the fiber optics contained within probe tip 1 includes a single lightsource fiber optic and three light receiver fiber optics. The use ofsuch fiber optics to measure the color of an object will be describedlater herein. Probe tip 1 is attached to probe body 2, on which is fixedswitch 17. Switch 17 communicates with microprocessor 10 through wire 18and provides, for example, a mechanism by which an operator may activatethe device in order to make a color measurement. Fiber optics withinprobe tip 1 terminate at the forward end thereof (i.e., the end awayfrom probe body 2). The forward end of probe tip 1 is directed towardsthe surface of the object to be measured as described more fully below.The fiber optics within probe tip 1 optically extend through probe body2 and through fiber optic cable 3 to light sensors 8, which are coupledto microprocessor 10.

It should be noted that microprocessor 10 includes conventionalassociated components, such as memory (programmable memory, such asPROM, EPROM or EEPROM; working memory such as DRAMs or SRAMs; and/orother types of memory such as nonvolatile memory, such as FLASH),peripheral circuits, clocks and power supplies, although for claritysuch components are not explicitly shown. Other types of computingdevices (such as other microprocessor systems, programmable logic arraysor the like) are used in other embodiments of the present invention.

In the embodiment of FIG. 1, the fiber optics from fiber optic cable 3end at splicing connector 4. From splicing connector 4, each of thethree receiver fiber optics used in this embodiment is spliced into atleast five smaller fiber optics (generally denoted as fibers 7), whichin this embodiment are fibers of equal diameter, but which in otherembodiments may be of unequal diameter (such as a larger or smaller“height/angle” or perimeter fiber, as more fully described herein). Oneof the fibers of each group of five fibers passes to light sensors 8through a neutral density filter (as more fully described with referenceto FIG. 3), and collectively such neutrally filtered fibers are utilizedfor purposes of height/angle determination (and also may be utilized tomeasure surface characteristics, as more fully described herein). Fourof the remaining fibers of each group of fibers passes to light sensors8 through color filters and are used to make the color measurement. Instill other embodiments, splicing connector 4 is not used, and fiberbundles of, for example, five or more fibers each extend from lightsensors 8 to the forward end of probe tip 1. In certain embodiments,unused fibers or other materials may be included as part of a bundle offibers for purposes of, for example, easing the manufacturing processfor the fiber bundle. What should be noted is that, for purposes of thepresent invention, a plurality of light receiver fiber optics (such asfibers 7) are presented to light sensors 8, with the light from thelight receiver fiber optics representing light reflected from object 20.While the various embodiments describe herein present tradeoffs andbenefits that may not have been apparent prior to the present invention(and thus may be independently novel), what is important for the presentdiscussion is that light from fiber optics at the forward end of probetip 1 is presented to color sensors 8 for color measurement andangle/height determination, etc.

Light source 11 in the preferred embodiment is a halogen light source(of, for example, 5-100 watts, with the particular wattage chosen forthe particular application), which may be under the control ofmicroprocessor 10. The light from light source 11 reflects from coldmirror 6 and into source fiber optic 5. Source fiber optic 5 passesthrough to the forward end of probe tip 1 and provides the lightstimulus used for purposes of making the measurements described herein.Cold mirror 6 reflects visible light and passes infra-red light, and isused to reduce the amount of infra-red light produced by light source 11before the light is introduced into source fiber optic 5. Such infra-redlight reduction of the light from a halogen source such as light source11 can help prevent saturation of the receiving light sensors, which canreduce overall system sensitivity. Fiber 15 receives light directly fromlight source 11 and passes through to light sensors 8 (which may bethrough a neutral density filter). Microprocessor 10 monitors the lightoutput of light source 11 through fiber 15, and thus may monitor and, ifnecessary compensate for, drift of the output of light source 11. Incertain embodiments, microprocessor 10 also may sound an alarm (such asthrough speaker 16) or otherwise provide some indication if abnormal orother undesired performance of light source 11 is detected.

The data output from light sensors 8 pass to microprocessor 10.Microprocessor 10 processes the data from light sensors 8 to produce ameasurement of color and/or other characteristics. Microprocessor 10also is coupled to key pad switches 12, which serve as an input device.Through key pad switches 12, the operator may input control informationor commands, or information relating to the object being measured or thelike. In general, key pad switches 12, or other suitable data inputdevices (such as push button, toggle, membrane or other switches or thelike), serve as a mechanism to input desired information tomicroprocessor 10.

Microprocessor 10 also communicates with UART 13, which enablesmicroprocessor 10 to be coupled to an external device such as computer13A. In such embodiments, color data provided by microprocessor 10 maybe processed as desired for the particular application, such as foraveraging, format conversion or for various display or print options,etc. In the preferred embodiment, UART 13 is configured so as to providewhat is known as a RS232 interface, such as is commonly found inpersonal computers.

Microprocessor 10 also communicates with LCD 14 for purposes ofdisplaying status, control or other information as desired for theparticular application. For example, color bars, charts or other graphicrepresentations of the color or other collected data and/or the measuredobject or tooth may be displayed. In other embodiments, other displaydevices are used, such as CRTs, matrix-type LEDs, lights or othermechanisms for producing a visible indicia of system status or the like.Upon system initialization, for example, LCD 14 may provide anindication that the system is stable, ready and available for takingcolor measurements.

Also coupled to microprocessor 10 is speaker 16. Speaker 16, in apreferred embodiment as discussed more fully below, serves to provideaudio feedback to the operator, which may serve to guide the operator inthe use of the device. Speaker 16 also may serve to provide status orother information alerting the operator of the condition of the system,including an audio tone, beeps or other audible indication (i.e., voice)that the system is initialized and available for taking measurements.Speaker 16 also may present audio information indicative of the measureddata, shade guide or reference values corresponding to the measureddata, or an indication of the status of the color measurements.

Microprocessor 10 also receives an input from temperature sensor 9.Given that many types of filters (and perhaps light sources or othercomponents) may operate reliably only in a given temperature range,temperature sensor 9 serves to provide temperature information tomicroprocessor 10. In particular, color filters, such as may be includedin light sensors 8, are sensitive to temperature, and operate reliablyonly over a certain temperature range. In certain embodiments, if thetemperature is within a usable range, microprocessor 10 may compensatefor temperature variations of the color filters. In such embodiments,the color filters are characterized as to filtering characteristics as afunction of temperature, either by data provided by the filtermanufacturer, or through measurement as a function of temperature. Suchfilter temperature compensation data may be stored in the form of alook-up table in memory, or may be stored as a set of polynomialcoefficients from which the temperature characteristics of the filtersmay be computed by microprocessor 10.

In general, under control of microprocessor 10, which may be in responseto operator activation (through, for example, key pad switches 12 orswitch 17), light is directed from light source 11, and reflected fromcold mirror 6 through source fiber optic 5 (and through fiber opticcable 3, probe body 2 and probe tip 1) and is directed onto object 20.Light reflected from object 20 passes through the receiver fiber opticsin probe tip 1 to light sensors 8 (through probe body 2, fiber opticcable 3 and fibers 7). Based on the information produced by lightsensors 8, microprocessor 10 produces a color measurement result orother information to the operator. Color measurement or other dataproduced by microprocessor 10 may be displayed on display 14, passedthrough UART 13 to computer 13A, or used to generate audio informationthat is presented to speaker 16. Other operational aspects of thepreferred embodiment illustrated in FIG. 1 will be explainedhereinafter.

With reference to FIG. 2, a preferred embodiment of the fiber opticarrangement presented at the forward end of probe tip 1 will now bedescribed. As illustrated in FIG. 2, a preferred embodiment of thepresent invention utilizes a single central light source fiber optic,denoted as light source fiber optic S, and a plurality of perimeterlight receiver fiber optics, denoted as light receivers R1, R2 and R3.As is illustrated, a preferred embodiment of the present inventionutilizes three perimeter fiber optics, although in other embodimentstwo, four or some other number of receiver fiber optics are utilized. Asmore fully described herein, the perimeter light receiver fiber opticsserve not only to provide reflected light for purposes of making thecolor measurement, but such perimeter fibers also serve to provideinformation regarding the angle and height of probe tip 1 with respectto the surface of the object that is being measured, and also mayprovide information regarding the surface characteristics of the objectthat is being measured.

In the illustrated preferred embodiment, receiver fiber optics R1 to R3are positioned symmetrically around source fiber optic S, with a spacingof about 120 degrees from each other. It should be noted that spacing tis provided between receiver fiber optics R1 to R3 and source fiberoptic S. While the precise angular placement of the receiver fiberoptics around the perimeter of the fiber bundle in general is notcritical, it has been determined that three receiver fiber opticspositioned 120 degrees apart generally may give acceptable results. Asdiscussed above, in certain embodiments light receiver fiber optics R1to R3 each constitute a single fiber, which is divided at splicingconnector 4 (refer again to FIG. 1), or, in alternate embodiments, lightreceiver fiber optics R1 to R3 each constitute a bundle of fibers,numbering, for example, at least five fibers per bundle. It has beendetermined that, with available fibers of uniform size, a bundle of, forexample, seven fibers may be readily produced (although as will beapparent to one of skill in the art, the precise number of fibers may bedetermined in view of the desired number of receiver fiber optics,manufacturing considerations, etc.). The use of light receiver fiberoptics R1 to R3 to produce color measurements in accordance with thepresent invention is further described elsewhere herein, although it maybe noted here that receiver fiber optics R1 to R3 may serve to detectwhether, for example, the angle of probe tip 1 with respect to thesurface of the object being measured is at 90 degrees, or if the surfaceof the object being measured contains surface texture and/or spectralirregularities. In the case where probe tip 1 is perpendicular to thesurface of the object being measured and the surface of the object beingmeasured is a diffuse reflector, then the light intensity input into theperimeter fibers should be approximately equal. It also should be notedthat spacing t serves to adjust the optimal height at which colormeasurements should be made (as more fully described below), and alsoensures that the light reflected into receiver fiber optics R1 to R3 isat an angle for diffuse reflection, which helps to reduce problemsassociated with measurements of “hot spots” on the surface of the objectbeing measured.

In one particular aspect of the present invention, area between thefiber optics on probe tip 1 may be wholly or partially filled with anon-reflective material and/or surface (which may be a black mat,contoured or other non-reflective surface). Having such exposed area ofprobe tip 1 non-reflective helps to reduce undesired reflections,thereby helping to increase the accuracy and reliability of the presentinvention.

With reference to FIG. 3, a partial arrangement of light receiver fiberoptics and sensors used in a preferred embodiment of the presentinvention will now be described. Fibers 7 represent light receivingfiber optics, which transmit light reflected from the object beingmeasured to light sensors 8. In a preferred embodiment, sixteen sensors(two sets of eight) are utilized, although for ease of discussion only 8are illustrated in FIG. 3 (in this preferred embodiment, the circuitryof FIG. 3 is duplicated, for example, in order to result in sixteensensors). In other embodiments, other numbers of sensors are utilized inaccordance with the present invention.

Light from fibers 7 is presented to sensors 8, which in a preferredembodiment pass through filters 22 to sensing elements 24. In thispreferred embodiment, sensing elements 24 include light-to-frequencyconverters, manufactured by Texas Instruments and sold under the partnumber TSL230. Such converters constitute, in general, photo diodearrays that integrate the light received from fibers 7 and output an ACsignal with a frequency proportional to the intensity (not frequency) ofthe incident light. Without being bound by theory, the basic principleof such devices is that, as the intensity increases, the integratoroutput voltage rises more quickly, and the shorter the integrator risetime, the greater the output frequency. The outputs of the TSL230sensors are TTL or CMOS compatible digital signals, which may be coupledto various digital logic devices.

The outputs of sensing elements 24 are, in this embodiment, asynchronoussignals of frequencies depending upon the light intensity presented tothe particular sensing elements, which are presented to processor 26. Ina preferred embodiment, processor 26 is a Microchip PIC16C55microprocessor, which as described more fully herein implements analgorithm to measure the frequencies of the signals output by sensingelements 24.

As previously described, processor 26 measures the frequencies of thesignals output from sensing elements 24. In a preferred embodiment,processor 26 implements a software timing loop, and at periodicintervals processor 26 reads the states of the outputs of sensingelements 24. An internal counter is incremented each pass through thesoftware timing loop. The accuracy of the timing loop generally isdetermined by the crystal oscillator time base (not shown in FIG. 3)coupled to processor 26 (such oscillators typically are quite stable).After reading the outputs of sensing elements 24, processor 26 performsan exclusive OR (“XOR”) operation with the last data read (in apreferred embodiment such data is read in byte length). If any bit haschanged, the XOR operation will produce a 1, and, if no bits havechanged, the XOR operation will produce a 0. If the result is non-zero,the input byte is saved along with the value of the internal counter(that is incremented each pass through the software timing loop). If theresult is zero, the systems waits (e.g., executes no operationinstructions) the same amount of time as if the data had to be saved,and the looping operation continues. The process continues until alleight inputs have changed at least twice, which enables measurement of afull ½ period of each input. Upon conclusion of the looping process,processor 26 analyzes the stored input bytes and internal counterstates. There should be 2 to 16 saved inputs (for the 8 total sensors ofFIG. 3) and counter states (if two or more inputs change at the sametime, they are saved simultaneously). As will be understood by one ofskill in the art, the stored values of the internal counter containsinformation determinative of the period of the signals received fromsensing elements 24. By proper subtraction of internal counter values attimes when an input bit has changed, the period may be calculated. Suchperiods calculated for each of the outputs of sensing elements isprovided by processor 26 to microprocessor 10 (see, e.g., FIG. 1). Fromsuch calculated periods, a measure of the received light intensities maybe calculated.

It should be noted that the sensing circuitry and methodologyillustrated in FIG. 3 have been determined to provide a practical andexpedient manner in which to measure the light intensities received bysensing elements 24. In other embodiments, other circuits andmethodologies are employed (other exemplary sensing schemes aredescribed elsewhere herein).

As discussed above with reference to FIG. 1, one of fibers 7 measureslight source 11, which may be through a neutral density filter, whichserves to reduce the intensity of the received light in order maintainthe intensity roughly in the range of the other received lightintensities. Three of fibers 7 also are from perimeter receiver fiberoptics R1 to R3 (see, e.g., FIG. 2) and also may pass through neutraldensity filters. Such receiving fibers 7 serve to provide data fromwhich angle/height information and/or surface characteristics may bedetermined.

The remaining twelve fibers (of the preferred embodiment's total of 16fibers) of fibers 7 pass through color filters and are used to producethe color measurement. In a preferred embodiment, the color filters areKodak Sharp Cutting Wratten Gelatin Filters, which pass light withwavelengths greater than the cut-off value of the filter (i.e., reddishvalues), and absorb light with wavelengths less than the cut-off valueof the filter (i.e., bluish values). “Sharp Cutting” filters areavailable in a wide variety of cut-off frequencies/wavelengths, and thecut-off values generally may be selected by proper selection of thedesired cut-off filter. In a preferred embodiment, the filter cut-offvalues are chosen to cover the entire visible spectrum and, in general,to have band spacings of approximately the visible band range (or otherdesired range) divided by the number of receivers/filters. As anexample, 700 nanometers minus 400 nanometers, divided by 11 bands(produced by twelve color receivers/sensors), is roughly 30 nanometerband spacing.

With an array of cut-off filters as described above, and without beingbound by theory or the specific embodiments described herein, thereceived optical spectrum may be measured/calculated by subtracting thelight intensities of “adjacent” color receivers. For example, band 1(400 nm to 430 nm)=(intensity of receiver 12) minus (intensity ofreceiver 11), and so on for the remaining bands. Such an array ofcut-off filters, and the intensity values that may result from filteringwith such an array, are more fully described in connection with FIGS.13A to 14B.

In a preferred embodiment of the present invention, the specificcharacteristics of the light source, filters, sensors and fiber optics,etc., are normalized/calibrated by directing the probe towards, andmeasuring, a known color standard. Such normalization/calibration may beperformed by placing the probe in a suitable fixture, with the probedirected from a predetermined position (i.e., height and angle) from theknown color standard. Such measured normalization/calibration data maybe stored, for example, in a look-up table, and used by microprocessor10 to normalize or correct measured color or other data. Such proceduresmay be conducted at start-up, at regular periodic intervals, or byoperator command, etc.

What should be noted from the above description is that the receivingand sensing fiber optics and circuitry illustrated in FIG. 3 provide apractical and expedient way to determine the intensity by color of thelight reflected from the surface of the object being measured.

It also should be noted that such a system measures the spectral band ofthe reflected light from the object, and once measured such spectraldata may be utilized in a variety of ways. For example, such spectraldata may be displayed directly as intensity-wavelength band values. Inaddition, tristimulus type values may be readily computed (through, forexample, conventional matrix math), or any other desired color values.In one particular embodiment useful in dental applications (such as fordental prostheses), the color data is output in the form of a closestmatch or matches of dental shade guide value(s). In a preferredembodiment, various existing shade guides (such as the shade guidesproduced by Vita Zahnfabrik) are characterized and stored in a look-uptable, and the color measurement data are used to select the closestshade guide value. In still other embodiments, the color measurementdata are used (such as with look-up tables) to select materials for thecomposition of paint or ceramics such as for prosthetic teeth. There aremany other uses of such spectral data measured in accordance with thepresent invention.

It is known that certain objects such as human teeth may fluoresce, andsuch characteristics also may be measured in accordance with the presentinvention. A light source with an ultraviolet component may be used toproduce more accurate color data of such objects. In certainembodiments, a tungsten/halogen source (such as used in a preferredembodiment) may be combined with a UV light source (such as a mercuryvapor, xenon or other fluorescent light source, etc.) to produce a lightoutput capable of causing the object to fluoresce. Alternately, aseparate UV light source, combined with a visible-light-blocking filter,may be used to illuminate the object. Such a UV light source may becombined with light from a red LED (for example) in order to provide avisual indication of when the UV light is on and also to serve as an aidfor the directional positioning of the probe operating with such a lightsource. A second measurement may be taken using the UV light source in amanner analogous to that described earlier, with the band of the red LEDor other supplemental light source being ignored. The second measurementmay thus be used to produce an indication of the fluorescence of thetooth or other object being measured. With such a UV light source, asilica fiber optic (or other suitable material) typically would berequired to transmit the light to the object (standard fiber opticmaterials such as glass and plastic do not propagate UV light in adesired manner, etc.).

As described earlier, the present invention utilizes a plurality ofperimeter receiver fiber optics spaced apart from and around a centralsource fiber optic to measure color and determine information regardingthe height and angle of the probe with respect to the surface of theobject being measured, which may include surface characteristicinformation, etc. Without being bound by theory, a principle underlyingthis aspect of the present invention will now be described withreference to FIGS. 4A to 4C.

FIG. 4A illustrates a typical step index fiber optic consisting of acore and a cladding. For this discussion, it is assumed that the corehas an index of refraction of no and the cladding has an index ofrefraction of n₁. Although the following discussion is directed to “stepindex” fibers, it will be appreciated by those of skill in the art thatsuch discussion generally is applicable for gradient index fibers aswell.

In order to propagate light without loss, the light must be incidentwithin the core of the fiber optic at an angle less than the criticalangle, phi, where phi=Sin⁻¹ {n₁/n₀}, where n₀ is the index of refractionof the core and n₁ is the index of refraction of the cladding. Thus, alllight must enter the fiber at an angle less than the critical angle, orit will not be propagated in a desired manner.

For light entering a fiber optic, it must enter within the acceptanceangle phi. Similarly, when the light exits a fiber optic, it will exitthe fiber optic within a cone of angle phi as illustrated in FIG. 4A.The ratio of the index of refraction of the cladding and core {n₁/n₀} isreferred to as the aperture of the fiber optic. Typical fiber opticshave an aperture of 0.5, and thus an acceptance/critical angle of 60°.

Consider using a fiber optic as a light source. One end is illuminatedby a light source (such as light source 11 of FIG. 1), and the other isheld near a surface. The fiber optic will emit a cone of light asillustrated in FIG. 4A. If the fiber optic is held perpendicular to asurface it will create a circular light pattern on the surface. As thefiber optic is raised, the radius r of the circle will increase. As thefiber optic is lowered, the radius of the light pattern will decrease.Thus, the intensity of the light (light energy per unit area) in theilluminated circular area will increase as the fiber optic is loweredand will decrease as the fiber optic is raised.

The same principle generally is true for a fiber optic being utilized asa receiver. Consider mounting a light sensor on one end of a fiber opticand holding the other end near an illuminated surface. The fiber opticcan only propagate light without loss when the light entering the fiberoptic is incident on the end of the fiber optic near the surface if thelight enters the fiber optic within its acceptance angle phi. A fiberoptic utilized as a light receiver near a surface will only accept andpropagate light from the circular area of radius r on the surface. Asthe fiber optic is raised from the surface, the area increases. As thefiber optic is lowered to the surface, the area decreases.

Consider two fiber optics parallel to each other as illustrated in FIG.4B. For simplicity of discussion, the two fiber optics illustrated areidentical in size and aperture. The following discussion, however,generally would be applicable for fiber optics that differ in size andaperture. One fiber optic is a source fiber optic, the other fiber opticis a receiver fiber optic. As the two fiber optics are heldperpendicular to a surface, the source fiber optic emits a cone of lightthat illuminates a circular area of radius r. The receiver fiber opticcan only accept light that is within its acceptance angle phi, or onlylight that is received within a cone of angle phi. If the only lightavailable is that emitted by the source fiber optic, then the only lightthat can be accepted by the receiver fiber optic is the light thatstrikes the surface at the intersection of the two circles asillustrated in FIG. 4C. As the two fiber optics are lifted from thesurface, the proportion of the intersection of the two circular areasrelative to the circular area of the source fiber optic increases. Asthey near the surface, the proportion of the intersection of the twocircular areas to the circular area of the source fiber optic decreases.If the fiber optics are held too close to the surface, the circularareas will no longer intersect and no light emitted from the sourcefiber optic will be received by the receiver fiber optic.

As discussed earlier, the intensity of the light in the circular areailluminated by the source fiber increases as the fiber is lowered to thesurface. The intersection of the two cones, however, decreases as thefiber optic pair is lowered. Thus, as the fiber optic pair is lowered toa surface, the total intensity of light received by the receiver fiberoptic increases to a maximal value, and then decreases sharply as thefiber optic pair is lowered still further to the surface. Eventually,the intensity will decrease essentially to zero (assuming the objectbeing measured is not translucent, as described more fully herein), andwill remain essentially zero until the fiber optic pair is in contactwith the surface. Thus, as a source-receiver pair of fiber optics asdescribed above are positioned near a surface and as their height isvaried, the intensity of light received by the receiver fiber opticreaches a maximal value at a critical height h_(c).

Again without being bound by theory, an interesting property of thecritical height h_(c) has been observed. The critical height h_(c) is afunction primarily of the geometry of fixed parameters, such as fiberapertures, fiber diameters and fiber spacing. Since the receiver fiberoptic in the illustrated arrangement is only detecting a maximum valueand not attempting to quantify the value, its maximum is independent ofthe surface characteristics. It is only necessary that the surfacereflect sufficient light from the intersecting area of the source andreceiver fiber optics to be within the detection range of the receiverfiber optic light sensor. Thus, red or green or blue or any colorsurface will all exhibit a maximum at the same critical height h_(c).Similarly, smooth reflecting surfaces and rough surfaces also will havevarying intensity values at the maximal value, but generally speakingall such surfaces will exhibit a maximum at the same critical heighth_(c). The actual value of the light intensity will be a function of thecolor of the surface and of the surface characteristics, but the heightwhere the maximum intensity value occurs in general will not.

Although the above discussion has focused on two fiber opticsperpendicular to a surface, similar analysis is applicable for fiberoptic pairs at other angles. When a fiber optic is not perpendicular toa surface, it generally illuminates an elliptical area. Similarly, theacceptance area of a receiver fiber optic generally becomes elliptical.As the fiber optic pair is moved closer to the surface, the receiverfiber optic also will detect a maximal value at a critical heightindependent of the surface color or characteristics. The maximalintensity value measured when the fiber optic pair is not perpendicularto the surface, however, will be less than the maximal intensity valuemeasured when the fiber optic pair is perpendicular to the surface.

Referring now to FIGS. 5A and 5B, the intensity of light received as afiber optic source-receiver pair is moved to and from a surface will nowbe described. FIG. 5A illustrates the intensity of the received light asa function of time. Corresponding FIG. 5B illustrates the height of thefiber optic pair from the surface of the object being measured. FIGS. 5Aand 5B illustrate (for ease of discussion) a relatively uniform rate ofmotion of the fiber optic pair to and from the surface of the objectbeing measured (although similar illustrations/analysis would beapplicable for non-uniform rates as well).

FIG. 5A illustrates the intensity of received light as the fiber opticpair is moved to and then from a surface. While FIG. 5A illustrates theintensity relationship for a single receiver fiber optic, similarintensity relationships would be expected to be observed for otherreceiver fiber optics, such as, for example, the multiple receiver fiberoptics of FIGS. 1 and 2. In general with the preferred embodimentdescribed above, all fifteen fiber optic receivers (of fibers 7) willexhibit curves similar to that illustrated in FIG. 5A.

FIG. 5A illustrates five regions. In region 1, the probe is movedtowards the surface of the object being measured, which causes thereceived light intensity to increase. In region 2, the probe is movedpast the critical height, and the received light intensity peaks andthen falls off sharply. In region 3, the probe essentially is in contactwith the surface of the object being measured. As illustrated, thereceived intensity in region 3 will vary depending upon the translucenceof the object being measured. If the object is opaque, the receivedlight intensity will be very low, or almost zero (perhaps out of rangeof the sensing circuitry). If the object is translucent, however, thelight intensity will be quite high, but in general should be less thanthe peak value. In region 4, the probe is lifted and the light intensityrises sharply to a maximum value. In region 5, the probe is liftedfurther away from the object, and the light intensity decreases again.

As illustrated, two peak intensity values (discussed as P1 and P2 below)should be detected as the fiber optic pair moves to and from the objectat the critical height h_(c). If peaks P1 and P2 produced by a receivefiber optic are the same value, this generally is an indication that theprobe has been moved to and from the surface of the object to bemeasured in a consistent manner. If peaks P1 and P2 are of differentvalues, then these may be an indication that the probe was not moved toand from the surface of the object in a desired manner, or that thesurface is curved or textured, as described more fully herein. In such acase, the data may be considered suspect and rejected. In addition,peaks P1 and P2 for each of the perimeter fiber optics (see, e.g., FIG.2) should occur at the same critical height (assuming the geometricattributes of the perimeter fiber optics, such as aperture, diameter andspacing from the source fiber optic, etc.). Thus, the perimeter fiberoptics of a probe moved in a consistent, perpendicular manner to andfrom the surface of the object being measured should have peaks P1 andP2 that occur at the same critical height. Monitoring receiver fibersfrom the perimeter receiver fiber optics and looking for simultaneous(or near simultaneous, e.g., within a predetermined range) peaks P1 andP2 provides a mechanism for determining if the probe is held at adesired perpendicular angle with respect to the object being measured.

In addition, the relative intensity level in region 3 serves as anindication of the level of translucency of the object being measured.Again, such principles generally are applicable to the totality ofreceiver fiber optics in the probe (see, e.g., fibers 7 of FIGS. 1 and3). Based on such principles, measurement techniques in accordance withthe present invention will now be described.

FIG. 6 is a flow chart illustrating a measuring technique in accordancewith the present invention. Step 49 indicates the start or beginning ofa color measurement. During step 49, any equipment initialization,diagnostic or setup procedures may be performed. Audio or visualinformation or other indicia may be given to the operator to inform theoperator that the system is available and ready to take a measurement.Initiation of the color measurement commences by the operator moving theprobe towards the object to be measured, and may be accompanied by, forexample, activation of switch 17 (see FIG. 1).

In step 50, the system on a continuing basis monitors the intensitylevels for the receiver fiber optics (see, e.g., fibers 7 of FIG. 1). Ifthe intensity is rising, step 50 is repeated until a peak is detected.If a peak is detected, the process proceeds to step 52. In step 52,measured peak intensity P1, and the time at which such peak occurred,are stored in memory (such as in memory included as a part ofmicroprocessor 10), and the process proceeds to step 54. In step 54, thesystem continues to monitor the intensity levels of the receiver fiberoptics. If the intensity is falling, step 54 is repeated. If a “valley”or plateau is detected (i.e., the intensity is no longer falling, whichgenerally indicates contact or near contact with the object), then theprocess proceeds to step 56. In step 56, the measured surface intensity(IS) is stored in memory, and the process proceeds to step 58. In step58, the system continues to monitor the intensity levels of the receiverfibers. If the intensity is rising, step 58 is repeated until a peak isdetected. If a peak is detected, the process proceeds to step 60. Instep 60, measured peak intensity P2, and the time at which such peakoccurred, are stored in memory, and the process proceeds to step 62. Instep 62, the system continues to monitor the intensity levels of thereceiver fiber optics. Once the received intensity levels begin to fallfrom peak P2, the system perceives that region 5 has been entered (see,e.g., FIG. 5A), and the process proceeds to step 64.

In step 64, the system, under control of microprocessor 10, may analyzethe collected data taken by the sensing circuitry for the variousreceiver fiber optics. In step 64, peaks P1 and P2 of one or more of thevarious fiber optics may be compared. If any of peaks P1 and P2 for anyof the various receiver fiber optics have unequal peak values, then thecolor data may be rejected, and the entire color measuring processrepeated. Again, unequal values of peaks P1 and P2 may be indicative,for example, that the probe was moved in a non-perpendicular orotherwise unstable manner (i.e., angular or lateral movement), and, forexample, peak P1 may be representative of a first point on the object,while peak P2 may be representative of a second point on the object. Asthe data is suspect, in a preferred embodiment of the present invention,color data taken in such circumstances are rejected in step 64.

If the data are not rejected in step 64, the process proceeds to step66. In step 66, the system analyzes the data taken from theneutral-density-filtered receivers from each of the perimeter fiberoptics (e.g., R1 to R3 of FIG. 2). If the peaks of the perimeter fiberoptics did not occur at or about the same point in time, this may beindicative, for example, that the probe was not held perpendicular tothe surface of the object being measured. As non-perpendicular alignmentof the probe with the surface of the object being measured may causesuspect results, in a preferred embodiment of the present invention,color data taken in such circumstances are rejected in step 66. In onepreferred embodiment, detection of simultaneous or near simultaneouspeaking (peaking within a predetermined range of time) serves as anacceptance criterion for the data, as perpendicular alignment generallyis indicated by simultaneous or near simultaneous peaking of theperimeter fiber optics. In other embodiments, step 66 includes ananalysis of peak values P1 and P2 of the perimeter fiber optics. In suchembodiments, the system seeks to determine if the peak values of theperimeter fiber optics (perhaps normalized with any initial calibrationdata) are equal within a defined range. If the peak values of theperimeter fiber optics are within the defined range, the data may beaccepted, and if not, the data may be rejected. In still otherembodiments, a combination of simultaneous peaking and equal valuedetection are used as acceptance/rejection criteria for the color data,and/or the operator may have the ability (such as through key padswitches 12) to control one or more of the acceptance criteria ranges.With such capability, the sensitivity of the system may be controllablyaltered by the operator depending upon the particular application andoperative environment, etc.

If the data are not rejected in step 66, the process proceeds to step68. In step 68, the color data may be processed in a desired manner toproduce output color measurement data. For example, such data may benormalized in some manner, or adjusted based on temperature compensationor other data detected by the system. The data also may be converted todifferent display or other formats, depending on the intended use of thecolor data. In addition, the data indicative of the translucence of theobject also may be quantified and/or displayed in step 68. After step68, the process may proceed to starting step 49, or the process may beterminated, etc.

In accordance the process illustrated in FIG. 6, three light intensityvalues (P1, P2 and PS) are stored per receiver fiber optic to make colorand translucency measurements. If stored peak values P1 and P2 are notequal (for some or all of the receivers), this is an indication that theprobe was not held steady over one area, and the data may be rejected(in other embodiments, the data may not be rejected, although theresulting data may be used to produce an average of the measured colordata). In addition, peak values P1 and P2 for the three neutral densityperimeter fiber optics should be equal or approximately equal; if thisis not the case, then this is an indication that the probe was not heldperpendicular or a curved surface is being measured. In otherembodiments, the system attempts to compensate for curved surfacesand/or non-perpendicular angles. In any event, if the system cannot makea color measurement, or if the data is rejected because peak values P1and P2 are unequal to an unacceptable degree, then the operator isnotified so that another measurement or other action may be taken (suchas adjust the sensitivity).

With a system constructed and operating as described above, colormeasurements may be taken of an object, with accepted color data havingheight and angular dependencies removed. Data not taken at the criticalheight, or data not taken with the probe perpendicular to the surface ofthe object being measured, etc., are rejected in a preferred embodimentof the present invention. In other embodiments, data received from theperimeter fiber optics may be used to calculate the angle of the probewith respect to the surface of the object being measured, and in suchembodiments non-perpendicular or curved surface color data may becompensated instead of rejected. It also should be noted that peakvalues P1 and P2 for the neutral density perimeter fiber optics providea measure of the luminance (gray value) of the surface of the objectbeing measured, and also may serve to quantify the color value.

The translucency of the object being measured may be quantified as aratio or percentage, such as, for example, (IS/P1)×100%. In otherembodiments, other methods of quantifying translucency data provided inaccordance with the present invention are utilized.

In another particular aspect of the present invention, data generated inaccordance with the present invention may be used to implement anautomated material mixing/generation machine. Certain objects/materials,such as dental prostheses, are made from porcelain or otherpowders/materials that may be combined in the correct ratios to form thedesired color of the object/prosthesis. Certain powders often containpigments that generally obey Beer's law and/or act in accordance withKubelka-Munk equations when mixed in a recipe. Color and other datataken from a measurement in accordance with the present invention may beused to determine or predict desired quantities of pigment or othermaterials for the recipe. Porcelain powders and other materials areavailable in different colors, opacities, etc. Certain objects, such asdental prostheses, may be layered to simulate the degree of translucencyof the desired object (such as to simulate a human tooth). Datagenerated in accordance with the present invention also may be used todetermine the thickness and position of the porcelain or other materiallayers to more closely produce the desired color, translucency, surfacecharacteristics, etc. In addition, based on fluorescence data for thedesired object, the material recipe may be adjusted to include a desiredquantity of fluorescing-type material. In yet other embodiments, surfacecharacteristics (such as texture) information (as more fully describedherein) may be used to add a texturing material to the recipe, all ofwhich may be carried out in accordance with the present invention.

For more information regarding such pigment-material recipe typetechnology, reference may be made to: “The Measurement of Appearance,”Second Edition, edited by Hunter and Harold, copyright 1987; “Principlesof Color Technology,” by Billmeyer and Saltzman, copyright 1981; and“Pigment Handbook,” edited by Lewis, copyright 1988. All of theforegoing are believed to have been published by John Wiley & Sons,Inc., New York, N.Y., and all of which are hereby incorporated byreference.

In certain operative environments, such as dental applications,contamination of the probe is of concern. In certain embodiments of thepresent invention, implements to reduce such contamination are provided.

FIGS. 7A and 7B illustrate a protective cap that may be used to fit overthe end of probe tip 1. Such a protective cap consists of body 80, theend of which is covered by optical window 82, which in a preferredembodiment consists of a structure having a thin sapphire window. In apreferred embodiment, body 80 consists of stainless steel. Body 80 fitsover the end of probe tip 1 and may be held into place by, for example,indentations formed in body 80, which fit with ribs 84 (which may be aspring clip or other retainer) formed on probe tip 1. In otherembodiments, other methods of affixing such a protective cap to probetip 1 are utilized. The protective cap may be removed from probe tip 1and sterilized in a typical autoclave, hot steam or other sterilizingsystem.

The thickness of the sapphire window should be less than the criticalheight of the probe in order to preserve the ability to detect peakingin accordance with the present invention. It also is believed thatsapphire windows may be manufactured in a reproducible manner, and thusany light attenuation from one cap to another may be reproducible. Inaddition, any distortion of the color measurements produced by thesapphire window may be calibrated out by microprocessor 10.

Similarly, in other embodiments body 80 has a cap with a hole in thecenter (as opposed to a sapphire window), with the hole positioned overthe fiber optic source/receivers. The cap with the hole serves toprevent the probe from coming into contact with the surface, therebyreducing the risk of contamination.

FIGS. 8A and 8B illustrate another embodiment of a removable probe tipthat may be used to reduce contamination in accordance with the presentinvention. As illustrated in FIG. 8A, probe tip 88 is removable, andincludes four (or a different number, depending upon the application)fiber optic connectors 90, which are positioned within optical guard 92.Optical guard 92 serves to prevent “cross talk” between adjacent fiberoptics. As illustrated in FIG. 8B, in this embodiment removable tip 88is secured in probe tip housing 92 by way of spring clip 96 (otherremovable retaining implements are utilized in other embodiments). Probetip housing 92 may be secured to base connector 94 by a screw or otherconventional fitting. It should be noted that, with this embodiment,different size tips may be provided for different applications, and thatan initial step of the process may be to install the properly-sized (orfitted tip) for the particular application. Removable tip 88 also may besterilized in a typical autoclave, hot steam or other sterilizingsystem. In addition, the entire probe tip assembly is constructed sothat it may be readily disassembled for cleaning or repair.

With reference to FIG. 9, a tristimulus embodiment of the presentinvention will now be described. In general, the overall system depictedin FIG. 1 and discussed in detail elsewhere herein may be used with thisembodiment. FIG. 9 illustrates a cross section of the probe tip fiberoptics used in this embodiment.

Probe tip 100 includes central source fiber optic 106, surrounded by(and spaced apart from) three perimeter receiver fiber optics 104 andthree color receiver fiber optics 102. Three perimeter receiver fiberoptics 104 are optically coupled to neutral density filters and serve asheight/angle sensors in a manner analogous to the embodiment describeabove. Three color receiver fiber optics are optically coupled tosuitable tristimulus filters, such as red, green and blue filters. Withthis embodiment, a measurement may be made of tristimulus color valuesof the object, and the process described with reference to FIG. 6generally is applicable to this embodiment. In particular, perimeterfiber optics 104 may be used to detect simultaneous peaking or otherwisewhether the probe is perpendicular to the object being measured. Inaddition, taking color measurement data at the critical height also maybe used with this embodiment.

FIG. 10A illustrates an embodiment of the present invention, similar tothe embodiment discussed with reference to FIG. 9. Probe tip 100includes central source fiber optic 106, surrounded by (and spaced apartfrom) three perimeter receiver fiber optics 104 and a plurality of colorreceiver fiber optics 102. The number of color receiver fiber optics102, and the filters associated with such receiver fiber optics 102, maybe chosen based upon the particular application. As with the embodimentof FIG. 9, the process described with reference to FIG. 6 generally isapplicable to this embodiment.

FIG. 10B illustrates an embodiment of the present invention in whichthere are a plurality of receiver fiber optics that surround centralsource fiber optic 240. The receiver fiber optics are arranged in ringssurrounding the central source fiber optic. FIG. 10B illustrates threerings of receiver fiber optics (consisting of fiber optics 242, 244 and246, respectively), in which there are six receiver fiber optics perring. The rings may be arranged in successive larger circles asillustrated to cover the entire area of the end of the probe, with thedistance from each receiver fiber optic within a given ring to thecentral fiber optic being equal (or approximately so). Central fiberoptic 240 is utilized as the light source fiber optic and is connectedto the light source in a manner similar to light source fiber optic 5illustrated in FIG. 1.

The plurality of receiver fiber optics are each coupled to two or morefiber optics in a manner similar to the arrangement illustrated in FIG.1 for splicing connector 4. One fiber optic from such a splicingconnector for each receiver fiber optic passes through a neutral densityfilter and then to light sensor circuitry similar to the light sensorcircuitry illustrated in FIG. 3. A second fiber optic from the splicingconnector per receiver fiber optic passes through a Sharp CuttingWrattan Gelatin Filter and then to light sensor circuitry as discussedelsewhere herein. Thus, each of the receiver fiber optics in the probetip includes both color measuring elements and neutral light measuringor “perimeter” elements.

FIG. 10D illustrates the geometry of probe 260 (such as described above)illuminating an area on flat diffuse surface 272. Probe 260 createslight pattern 262 that is reflected diffusely from surface 272 inuniform hemispherical pattern 270. With such a reflection pattern, thereflected light that is incident upon the receiving elements in theprobe will be equal (or nearly equal) for all elements if the probe isperpendicular to the surface as described above herein.

FIG. 10C illustrates a probe illuminating rough surface 268 or a surfacethat reflects light spectrally. Spectral reflected light will exhibithot spots or regions where the reflected light intensity is considerablygreater than it is on other areas. The reflected light pattern will beuneven when compared to a smooth surface as illustrate in FIG. 10D.

Since a probe as illustrated in FIG. 10B has a plurality of receiverfiber optics arranged over a large surface area, the probe may beutilized to determine the surface texture of the surface as well asbeing able to measure the color and translucency of the surface asdescribed earlier herein. If the light intensity received by thereceiver fiber optics is equal for all fiber optics within a given ringof receiver fiber optics, then generally the surface is diffuse andsmooth. If, however, the light intensity of receiver fibers in a ringvaries with respect to each other, then generally the surface is roughor spectral. By comparing the light intensities measured within receiverfiber optics in a given ring and from ring to ring, the texture andother characteristics of the surface may be quantified.

FIG. 11 illustrates an embodiment of the present invention in whichlinear optical sensors and a color gradient filter are utilized insteadof light sensors 8 (and filters 22, etc.). Receiver fiber optics 7,which may be optically coupled to probe tip 1 as with the embodiment ofFIG. 1, are optically coupled to linear optical sensor 112 through colorgradient filter 110. In this embodiment, color gradient filter 110 mayconsist of series of narrow strips of cut-off type filters on atransparent or open substrate, which are constructed so as topositionally correspond to the sensor areas of linear optical sensor112. An example of a commercially available linear optical sensor 112 isTexas Instruments part number TSL213, which has 61 photo diodes in alinear array. Light receiver fiber optics 7 are arranged correspondinglyin a line over linear optical sensor 112. The number of receiver fiberoptics may be chosen for the particular application, so long as enoughare included to more or less evenly cover the full length of colorgradient filter 110. With this embodiment, the light is received andoutput from receiver fiber optics 7, and the light received by linearoptical sensor 112 is integrated for a short period of time (determinedby the light intensity, filter characteristics and desired accuracy).The output of linear array sensor 112 is digitized by ADC 114 and outputto microprocessor 116 (which may the same processor as microprocessor 10or another processor).

In general, with the embodiment of FIG. 11, perimeter receiver fiberoptics may be used as with the embodiment of FIG. 1, and in general theprocess described with reference to FIG. 6 is applicable to thisembodiment.

FIG. 12 illustrates an embodiment of the present invention in which amatrix optical sensor and a color filter grid are utilized instead oflight sensors 8 (and filters 22, etc.). Receiver fiber optics 7, whichmay be optically coupled to probe tip 1 as with the embodiment of FIG.1, are optically coupled to matrix optical sensor 122 through filtergrid 120. Filter grid 120 is a filter array consisting of a number ofsmall colored spot filters that pass narrow bands of visible light.Light from receiver fiber optics 7 pass through corresponding filterspots to corresponding points on matrix optical sensor 122. In thisembodiment, matrix optical sensor 122 may be a monochrome optical sensorarray, such as CCD-type or other type of light sensor element such asmay be used in a video camera. The output of matrix optical sensor 122is digitized by ADC 124 and output to microprocessor 126 (which may thesame processor as microprocessor 10 or another processor). Under controlof microprocessor 126, matrix optical sensor 126 collects color datafrom receiver fiber optics 7 through color filter grid 120.

In general, with the embodiment of FIG. 12, perimeter receiver fiberoptics may be used as with the embodiment of FIG. 1, and in general theprocess described with reference to FIG. 6 also is applicable to thisembodiment.

As will be clear from the foregoing description, with the presentinvention a variety of types of spectral color photometers (ortristimulus-type calorimeters) may be constructed, with perimeterreceiver fiber optics used to collect color data essentially free fromheight and angular deviations. In addition, in certain embodiments, thepresent invention enables color measurements to be taken at a criticalheight from the surface of the object being measured, and thus colordata may be taken without physical contact with the object beingmeasured (in such embodiments, the color data is taken only by passingthe probe through region 1 and into region 2, but without necessarilygoing into region 3 of FIGS. 5A and 5B). Such embodiments may beutilized if contact with the surface is undesirable in a particularapplication. In the embodiments described earlier, however, physicalcontact (or near physical contact) of the probe with the object mayallow all five regions of FIGS. 5A and 5B to be utilized, therebyenabling color measurements to be taken such that translucencyinformation also may be obtained. Both types of embodiments generallyare within the scope of the invention described herein.

Additional description will now be provided with respect to cut-offfilters of the type described in connection with the preferredembodiment(s) of FIGS. 1 and 3 (such as filters 22 of FIG. 3). FIG. 13Aillustrates the properties of a single Kodak Sharp Cutting WrattenGelatin Filter discussed in connection with FIG. 3. Such a cut-offfilter passes light below a cut-off frequency (i.e., above a cut-offwavelength). Such filters may be manufactured to have a wide range ofcut-off frequencies/wavelengths. FIG. 13B illustrates a number of suchfilters, twelve in a preferred embodiment, with cut-offfrequencies/wavelengths chosen so that essentially the entire visibleband is covered by the collection of cut-off filters.

FIGS. 14A and 14B illustrate exemplary intensity measurements using acut-off filter arrangement such as illustrated in FIG. 13B, first in thecase of a white surface being measured (FIG. 14A), and also in the caseof a blue surface being measured (FIG. 14B). As illustrated in FIG. 14A,in the case of a white surface, the neutrally filtered perimeter fiberoptics, which are used to detect height and angle, etc., generally willproduce the highest intensity (although this depends at least in partupon the characteristics of the neutral density filters). As a result ofthe stepped cut-off filtering provided by filters having thecharacteristics illustrated in FIG. 13B, the remaining intensities willgradually decrease in value as illustrated in FIG. 14A. In the case of ablue surface, the intensities will decrease in value generally asillustrated in FIG. 14B. Regardless of the surface, however, theintensities out of the filters will always decrease in value asillustrated, with the greatest intensity value being the output of thefilter having the lowest wavelength cut-off value (i.e., passes allvisible light up to blue), and the lowest intensity value being theoutput of the filter having the highest wavelength cut-off (i.e., passesonly red visible light). As will be understood from the foregoingdescription, any color data detected that does not fit the decreasingintensity profiles of FIGS. 14A and 14B may be detected as anabnormality, and in certain embodiments detection of such a conditionresults in data rejection, generation of an error message or initiationof a diagnostic routine, etc.

Reference should be made to the FIGS. 1 and 3 and the relateddescription for a detailed discussion of how such a cut-off filterarrangement may be utilized in accordance with the present invention.

FIG. 15 is a flow chart illustrating audio tones that may be used incertain preferred embodiments of the present invention. It has beendiscovered that audio tones (such as tones, beeps, voice or the likesuch as will be described) present a particularly useful and instructivemeans to guide an operator in the proper use of a color measuring systemof the type described herein.

The operator may initiate a color measurement by activation of a switch(such as switch 17 of FIG. 1) at step 150. Thereafter, if the system isready (set-up, initialized, calibrated, etc.), a lower-the-probe tone isemitted (such as through speaker 16 of FIG. 1) at step 152. The systemattempts to detect peak intensity P1 at step 154. If a peak is detected,at step 156 a determination is made whether the measured peak P1 meetsthe applicable criteria (such as discussed above in connection withFIGS. 5A, 5B and 6). If the measured peak P1 is accepted, a first peakacceptance tone is generated at step 160. If the measured peak P1 is notaccepted, an unsuccessful tone is generated at step 158, and the systemmay await the operator to initiate a further color measurement. Assumingthat the first peak was accepted, the system attempts to detect peakintensity P2 at step 162. If a second peak is detected, at step 164 adetermination is made whether the measured peak P2 meets the applicablecriteria. If the measured peak P2 is accepted the process proceeds tocolor calculation step 166 (in other embodiments, a second peakacceptance tone also is generated at step 166). If the measured peak P2is not accepted, an unsuccessful tone is generated at step 158, and thesystem may await the operator to initiate a further color measurement.Assuming that the second peak was accepted, a color calculation is madeat step 166 (such as, for example, microprocessor 10 of FIG. 1processing the data output from light sensors 8, etc.). At step 168, adetermination is made whether the color calculation meets the applicablecriteria. If the color calculation is accepted, a successful tone isgenerated at step 170. If the color calculation is not accepted, anunsuccessful tone is generated at step 158, and the system may await theoperator to initiate a further color measurement.

With unique audio tones presented to an operator in accordance with theparticular operating state of the system, the operator's use of thesystem may be greatly facilitated. Such audio information also tends toincrease operator satisfaction and skill level, as, for example,acceptance tones provide positive and encouraging feedback when thesystem is operated in a desired manner.

As will be apparent to those skilled in the art, certain refinements maybe made in accordance with the present invention. For example, a centrallight source fiber optic is utilized in certain preferred embodiments,but other light source arrangements (such as a plurality of light sourcefibers, etc.). In addition, lookup tables are utilized for variousaspects of the present invention, but polynomial type calculations couldsimilarly be employed. Thus, although various preferred embodiments ofthe present invention have been disclosed for illustrative purposes,those skilled in the art will appreciate that various modifications,additions and/or substitutions are possible without departing from thescope and spirit of the present invention as disclosed in the claims.

Reference is also made to copending application Ser. No. 08/582,054,filed Jan. 2, 1996, now U.S. Pat. No. 5,759,030, for “Apparatus andMethod for Measuring the Color of Teeth,” by the inventors hereof, whichis hereby incorporated by reference.

1. A method in a spectral measurement apparatus comprising the steps of:receiving light with a plurality of sensors, wherein each sensorgenerates an output signal having a frequency proportional to anintensity of light received by the sensor; generating at least a firstsignal having a frequency proportional to an intensity of light receivedby a first sensor of a first wavelength or spectral band; generating atleast a second signal having a frequency proportional to an intensity oflight received by a second sensor of a second wavelength or spectralband; and generating at least a third signal having a frequencyproportional to an intensity of light received by a third sensor of athird wavelength or spectral band; wherein a spectral characteristic ofthe received light is determined based on at least the first, second andthird signals; wherein the at least first, second and third signals arecoupled to a processing element and input to the processing element inparallel, wherein the spectral characteristic is determined based onmeasuring a frequency or period of the at least first, second and thirdsignals; wherein spectral data based on the determined spectralcharacteristic is generated by the processing element and displayed on adisplay device for perception by a viewer or transmitted to a datainterface for transmission to an electronic device external to thespectral measurement apparatus.
 2. The method of claim 1, wherein thesensors each output one or more digital signals.
 3. The method of claim2, wherein the one or more digital signals comprise TTL or CMOScompatible signals.
 4. The method of claim 3, wherein the one or moredigital signals are coupled to a microprocessor or logic circuitrywithout analog-to-digital conversion.
 5. The method of claim 1, whereinthe spectral characteristic is determined based on measuring a frequencyof the at least first, second and third signals.
 6. The method of claim1, wherein the spectral characteristic is determined based on measuringa period of the at least first, second and third signals.
 7. The methodof claim 1, wherein the spectral measurement apparatus comprises aspectrometer.
 8. The method of claim 1, wherein the spectral measurementapparatus comprises a colorimeter.
 9. The method of claim 1, whereinlight is received from an object or material via one or more fiberoptics.
 10. The method of claim 1, wherein the spectral characteristicis determined based on a calibration measurement.
 11. The method ofclaim 1, wherein the spectral characteristic is used to determine aclosest color among a set of stored colors.
 12. The method of claim 1,wherein the light is generated via a broadband light source.
 13. Themethod of claim 1, wherein the light is generated via a plurality oflight sources of different colors.
 14. The method of claim 1, whereinthe processing element determines a plurality of data values from thefirst, second and third signals at a predetermined timing, wherein,based on the plurality of data values determined from the first, secondand third signals, a frequency or period determination is made for eachof the first, second and third signals.
 15. The method of claim 1,wherein the sensors each comprise an array of photodiodes.
 16. Themethod of claim 1, wherein the spectral characteristic is used todetermine one or more closest matches to a plurality of stored colors orshades, wherein the stored colors or shades comprise shades of one ormore dental shade guide systems.
 17. The method of claim 1, wherein theprocessing element is coupled to a light source, wherein the lightsource is controlled based on a signal from the processing element. 18.A method in a spectral measurement apparatus for determining a spectralcharacteristic of received light comprising the steps of: generating andsupplying light of a plurality of wavelengths or spectral bands;receiving light with a plurality of sensors, wherein each sensorgenerates an output signal having a frequency proportional to anintensity of light received by the sensor; generating at least a firstsignal having a frequency proportional to an intensity of light receivedby a first sensor of a first wavelength or spectral band; generating atleast a second signal having a frequency proportional to an intensity oflight received by a second sensor of a second wavelength or spectralband; and generating at least a third signal having a frequencyproportional to an intensity of light received by a third sensor of athird wavelength or spectral band; wherein a spectral characteristic ofthe received light is determined based on at least the first, second andthird signals; wherein the at least first, second and third signals arecoupled to a processing element and input to the processing element inparallel, wherein the spectral characteristic is determined based onmeasuring a frequency or period of the at least first, second and thirdsignals; wherein spectral data based on the determined spectralcharacteristic is generated by the processing element and displayed on adisplay device for perception by a viewer or transmitted to a datainterface for transmission to an electronic device external to thespectral measurement apparatus.
 19. The method of claim 18, wherein thespectral measurement apparatus comprises a spectrometer.
 20. The methodof claim 18, wherein the processing element is coupled to a lightsource, wherein the light source is controlled based on a signal fromthe processing element.